Multiple Stressors and Amphibians: Contributions of Adverse Health Effects and Altered Hydroperiod to Population Decline and Extinction

Amphibian decline is a well-recognized globally occurring problem. Hypothesized and demonstrated causes of decline are varied and include disease, contaminants, habitat loss, and climate change. Future research and management efforts may be further improved by understanding how different anthropogenic stress factors contribute to amphibian population declines for different species. I used a stochastic, density-dependent population model of the pool-breeding amphibian, Gastrophryne carolinensis, to explore the relative contribution of different simulated stress factors operating individually and in combination on a number of different life-cycle components. The simulations revealed that catastrophic reproductive failure (CRF) as may occur under climate-induced reductions in hydroperiod was a strong driver of extinction risk and that, in the absence of CRF, extinction risks were low (<1%) even under some reduction in recruitment and terrestrial survival for this species. When reductions in vital rates and CRF occurred together, extinction risks increased pointing to the importance of multiple factors as potential drivers of amphibian decline. The results presented here suggest that climate change-induced alterations in hydroperiod may have severe consequences for declines of some amphibian populations. Further, the presence of additional stress factors only serves to increase risk. In addition to the need for studies of stressor effects on components of amphibian life cycles, future research and conservation efforts should consider the interaction of stressors acting on the health of individuals (disease, pollution) and temporal variation in environmental factors such as hydroperiod.